WASHINGTON – Lockheed Martin political action committees and employees have contributed generously to members of Congress, including two Vermont lawmakers, since winning the main contract to develop the Joint Strike Fighter jet, the most expensive weapons project ever.

PACs and employees affiliated with Lockheed contributed $12.4 million to members of Congress between Jan. 1, 2001 and Dec. 31, 2013, according to a recent MapLight analysis of contributions compiled by OpenSecrets.org. About $8.1 million went to current members.

Sen. Patrick Leahy, D-Vt., received $12,000 and Rep. Peter Welch, D-Vt., received $5,200 during that period, according to MapLight, a research group that tracks money's influence on politics.

The Vermont Air National Guard will be the first Guard base to receive the planes, starting in 2020. Over heated objections from some Vermonters, both Leahy and Welch — along with Sen. Bernie Sanders, I-Vt. — strongly supported basing F-35s at the Air Guard station at Burlington International Airport. The analysis shows no Lockheed-related contributions for Sanders, who does not accept corporate PAC contributions.

MapLight notes that the F-35 project has repeatedly received federal appropriations from Congress despite a string of technical problems and failures to deliver functioning planes on time and within budget. The project is expected to cost about $1.5 trillion. Last month, Senate appropriators, including Leahy, approved a fiscal 2015 defense spending bill that included more money for the planes.

The MapLight analysis offers a "clear example of how political contributions have a high return on investment," said Daniel G. Newman, the group's co-founder and president. The analysis shows that contributions to current and past members of Congress rose from $481,363 in 2001 to nearly $1.6 million in 2013.

"I don't think anyone would question there's an economy of influence on Capitol Hill," Newman said in a statement. "A strong dependency for money, in the form of campaign contributions, exists on both sides of the aisle. Until we have a political system where fundraising doesn't distort lawmaking, these unacceptable practices will continue."

Lockheed Martin spokesman Gordon Johndroe said in a statement that the Lockheed Martin Employees PAC "supports a variety of Representatives, Senators and organizations, from both sides of the aisle, that share our interest in a strong national defense."

Lockheed PACs and employees gave less to Leahy and Welch than to other lawmakers. Senate Minority Whip John Cornyn of Texas received $139,450, and Rep. Kay Granger, R-Texas, vice chairman of the House Appropriations Subcommittee on Defense, received $226,150, more than any member of Congress.

Vermont's three congressional lawmakers have long criticized the F-35 program's cost overruns and procurement process. They supported basing the plane in Vermont to preserve jobs as the Air Force retires aging F-16s flown by Vermont's 158th Fighter Wing.

Leahy, who co-chairs the Senate National Guard Caucus, took a special interest in the effort and called the Air Force chief of staff in 2013 for a status check.

Some Vermonters say the F-35s present an unacceptable risk of crashes and will hurt real-estate values and cause noise problems. Several filed a lawsuit aimed at stopping the Air Force from basing the planes in Vermont.

Rosanne Greco, a former South Burlington city councilor and F-35 opponent, questioned why Leahy and Welch, whose campaigns already are well-funded, would accept donations from Lockheed after criticizing defense spending and the F-35 procurement process.

"If they don't need it, and those corporations don't align with what they say their values are, why would you take their money?" she asked.

Spokesmen for the lawmakers did not specifically answer that question.

"Basing in Vermont for him has always been about recapitalizing (the Vermont Air National Guard,)" David Carle, Leahy's spokesman, wrote in an email. "The F-35 is the Air Force's future, and it's the plane of the future for VTANG. His skepticism about problems in the management of the program over the years is well documented."

Carle added that Leahy did not vote specifically to approve more money for the F-35 program when he voted last month for the fiscal 2015 defense appropriations bill. Leahy also did not sign a Senate letter calling for restoring the full number of planned F-35s.

Bob Rogan, Welch's chief of staff, said donations from Lockheed have not influenced Welch. Since Welch arrived in Congress in 2007, he has voted against all defense authorization and appropriations bills, Rogan said. Those bills authorized or contained money for the F-35 program.

He said Lockheed has never contacted Welch's office on issues related to the plane. However, Welch is a major proponent of energy efficiency and has worked with the company on a "shared agenda of making federal agencies as energy efficient as possible," Rogan said.

"Since the F-35 is the Pentagon's designated replacement for the F-16, and since it is currently in production, the congressman believes that it would be good for the Guard, the airport, jobs, and the regional economy if the new plane is based in South Burlington to replace the F-16s based there now," Rogan said in an email. "And he has repeatedly urged the Pentagon and the Guard to adjust operational plans to mitigate the concerns of nearby residents and businesses."